Artificial ion cloud



June 30, 1970 ALTITUDE (IN MILES) FIG.

A. MELLER ARTIFICIAL ION CLOUD Filed Sept. 25, 1967 %J SLIGHT 2 a I I I I INVENTOR. I l I I50 [220 270 300 ARNOLD MILLER zoo BY 8 TEMPERATURE A g (IN K) ATTORNEY United States Patent 3,518,670. Patented June 30, 1970 3,518,670 ARTIFICIAL ION CLOUD Arnold Miller, Fullerton, Califi, assignor to North American Rockwell Corporation Filed Sept. 25, 1967, Ser. No. 670,348 Int. Cl. H01q /18 US. Cl. 34318 10 Claims ABSTRACT OF THE DISCLOSURE Apparatus and method for producing in the ozone layer an artificial ion cloud having sufficient electron density to reflect electromagnetic waves. Ablative coated microspheres of lithium hydride, sodium hydride, butyl lithium, or ethyl cesium are released through a nozzle in a vehicle passing through the stratosphere. The coatings ablate and the exposed compounds photoionize at the ozone layer ambient temperature to produce an ion cloud. As charge is neutralized, reionization occurs by light absorption producing a long lifetime cloud. Typically, a cloud of 2.1 1(l cubic feet of ionized gas having a charge density of 10 electrons/cm. may be produced with 0.8 pound of lithium hydride.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to an apparatus and process for producing artificial ion cloud. More particularly, the invention relates to production of an ion cloud by release in the stratosphere of ablative coated microspheres of a compound which is photoionizable at ozone layer ambient temperatures.

Background of the invention Various applications exist for artificial ion clouds capable of refracting or reflecting electromagnetic radiation. For example, such clouds may be used to reflect radio signals between two points on the earth.

It is well known that meteor trails formed by ionization of ambient air at altitudes of about 56 to 68 miles exhibit radar cross-sections of 10 to 10 meter for frequencies between mHz. and 100 mHz. As described by I. S. Greenhow et al. (in the book entitled Physics of the Upper Atmosphere, J. A. Ratcliffe editor, Academic Press, New York, 1960, beginning at p. 544) meteor trail ionization is short-lived, the constituent electrons being lost by diffusion, radiative recombination and attachments to atoms or molecules. It is these diffusion, recombination and attachment mechanisms which in the past have severely limited the lifetime of an artificial ion cloud.

Prior art artificial ion clouds primarily have been of the explosive or thermal reaction type. Typically, a high altitude bursting rocket was used to fire potassium nitrate and aluminum into the ionosphere. An aluminothermic reaction occurred, typically of an altitude of about 62 miles, yielding elemental potassium, nitrogen gas and aluminum dust. The potassium vapor, with an ionization potential of 4.32 ev., is ionized in the high temperature reaction producing suflicient free electrons so as to reflect electromagnetic radiation. In daylight at this 62 mile altitude the neutral potassium is photoionized, extending the lifetime of the cloud.

An alternative approach of the prior art was to use an explosive charge of RDX with cesium nitrate and aluminum. The elemental cesium produced by the reaction has an ionization potential of 3.86 ev., hence is photoionizable in the ionosphere.

While these techniques were useful to produce an artificial ion cloud in the ionosphere, then exhibited disadvantages typical of explosive or thermal type reactions. For example, the percentage conversion of material into ions by explosive reaction is low, with much of the actual mass being converted into inert non-ionic products not useful for reflection of electromagnetic radiation. Since this net mass-to-change conversion is low, it is uneconomical to use these prior art techniques to produce artificial ion clouds. Moreover such prior art artificial ion clouds had to be produced at altitudes well above the stratosphere.

The present invention sets forth a technique and apparatus for producing an artificial ion cloud in the ozone layer, which cloud has a suflicient ion density to exhibit high reflectivity of electromagnetic waves. The technique has a high mass-to-change conversion factor and produces a cloud having a relatively long lifetime.

SUMMARY OF THE PRESENT INVENTION In accordance with the present invention, there is set forth an apparatus and process for producing an artificial ion cloud in the ozone layer (stratosphere), which cloud is capable of reflecting electromagnetic waves. The technique utilizes photoionization of lithium hydride, sodium hydride, butyl lithium, or ethyl cesium packaged as ablative coated microspheres.

The ablative coated microspheres are metered out of nozzles in a vehicle passing through the stratosphere. When released, the coating ablates permitting the reactant to photoionize at the ambient temperature of the ozone layer. For example, lithium hydride photoionizes to produce ionized elemental lithium and free electrons. As charge neutralizes in the artificial cloud thus produced, reionization occurs by light absorption, greatly increasing the lifetime of the cloud. Since the reaction follows homogeneous kinetics, essentially conversion may be achieved.

Thus it is an object of the present invention to provide an artificial ion cloud.

Another object of the present invention is to provide a technique for producing in the stratosphere an artifical ion cloud capable of refracting or reflecting electromagnetic radiation, and having relatively long lifetime.

Yet another object of the present invention is to provide an ion cloud in the ozone layer by continuous photoionization of lithium hydride, sodium hydride, butyl lithium, or ethyl cesium.

Another object of the present invention is to provide a technique for producing an artificial ion cloud by releasing into the upper atmosphere ablative coated microspheres of a compound which photoionizes at upper atmosphere ambient temperatures.

These and other objects and features of the present invention will become clear in conjunction with the following illustrative drawings and description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified perspective view, in partial section, of a vehicle equipped to produce an artificial ion cloud in accordance with the present invention. The vehicle is illustrated as passing through the stratosphere and behind it an ion cloud capable of reflecting electromagnetic radiation.

FIG. 2 is a greatly enlarged perspective view, in partial section, of a typical ablative covered microsphere containing a photoionizable compound useful for producing an artificial ion cloud in accordance with the present invention.

FIG. 3 is a graph of temperature as a function of altitude for various atmospheric regions.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates production of an artificial ion cloud 20 in accordance with the present invention. As shown in FIG. 1, vehicle 10 comprises a ballistic rocket, a satellite re-entry vehicle, or the like. Mounted within vehicle 10 is supply reservoir 12 which reservoir is adapted to store an appropriate quantity of free-flowing ablative coated microspheres 30. As described hereinbelow in conjunction with FIG. 2, microspheres 30 each contain a compound which photoionizes at the ambient temperature of the atmospheric level at which artificial ion cloud 20 is to be produced. Preferably, cloud 20 is produced in the ozone layer of the stratosphere, from about 10 miles to about 38 miles above sea level.

Vehicle 10 (see FIG. 1) is equipped with appropriate pump 14 or equivalent device for withdrawing microspheres 30 from reservoir 12 and for supplying them at a controlled rate to nozzle 16. Preferably microspheres 30 are emitted from nozzle 16 at a relatively uniform rate as vehicle 10 passes through the atmospheric layer in which cloud 20 is to be produced.

As illustrated in FIG. 1, microspheres 30 emitted from nozzle 16 form cloud 20 in the wake of vehicle 10. As microspheres 30 are shot from nozzle 16 they encounter sufiicient resistive force due to collisions with ozone and other atoms or molecules present in the stratosphere to cause ablation of the microsphere coating. This releases the photoionizable compound from microsphere 30, which compound photoionizes in the presence of sunlight 22 to produce free electrons. Artificial ion cloud 20 thus produced is of sufficient electron density as to be capable of reflecting electromagnetic radiation.

The manner in which artificial ion cloud 20 is produced may be understood more fully in conjunction with FIG. 2, which shows a greatly enlarged view of typical microsphere 30. The actual size of microsphere 30 is not critical, and typically is of millimeter range. Each microsphere 30 comprises a core 33 of a compound which is photoionizable at the ambient temperatures of the atmospheric region in which cloud 20 is to be produced. Core 33 is surrounded by ablative coating 34 which typically comprises a low melting microcrystalline wax. Of course, other ablative materials well known to those skilled in the art also may be used for coating 34. Although coating 34 is illustrated as being of uniform thickness, this is not a requisite of the invention.

Microspheres 30 may be produced by micro-encapsulation techniques well known to those skilled in the art, and typified by that described in the US. Patent to Brynko et al. Pat. No. 3,190,837. Such micro-encapsulation provides microspheres 30 which collectively have a free-flowing consistency not unlike granulated sugar. Individual microspheres 30 have coatings 34 of somewhat random thickness, resulting in correspondingly random ablation times when released from vehicle 10 in the stratosphere. This random ablation time aids in dispersion fo microspheres 30 to produce cloud 20 of maximal size.

Materials which have been found optimum for use as core 33 of microsphere 30 include lithium hydride (LiH), sodium hydride (NaH), butyl lithium (C H Li), or ethyl cesium (C H Cs). These are all extremely energetic compounds which photoionize by the following As indicated in the graph of FIG. 3, ambient temperature in the stratosphere range from about 220 K. to about 270 K. All of the compounds (LiH, NaH, C H Li and C H Cs) suggested hereinabove for use as microsphere core 33 will photoionize in this temperature range.

4 If microspheres 30 are appropriately metered out by nozzle 16 (see FIG. 1), a cloud 20 of about 2.l 10 cubic feet, having an average charge density of 10 electrons/cm. may be produced with the following amounts of photoionizable core 33 compound.

Amount Compound (in pounds) LiH 0. 8

NaH 2.4 C H Li 6.4 C2H5CS Typically, 0.8 pound of lithium hydride will provide 0.7 pound of ionized elemental lithium and yield about 5 10 free electrons. By distributing this into a cloud of 2.1 10 cubic feet, a charge density of 10 electrons/cm. may be obtained.

The ability of artificial ion cloud 2) to reflect electromagnetic radiation may be expressed in terms of its radar cross section. As discussed at p. 626 of the text Introduction of Radar Systems by Merrill I. Skolnick, Mc- Graw-Hill, New York, 1962, the radar cross section of an electron is defined as the power scattered into a unit solid angle per unit incident power density. For backscatter radar, o' =8 1O meters The cross section o' per unit volume of a cloud of electrons having a density of N electrons per cubic meter, all of which electrons scatter incoherently, is given by Substituting a value of N=lO /cm. =1O /m. into Equation 5 indicates that for a cloud of charge density 10 electrons/cm. the theoretical radar cross section will be o' =8 1O /m. a very considerable value.

The frequency f of a signal which would be totally reflected from an ion cloud having a charge density of 10 electrons/cm. may be found from the equation:

where N is the number of electrons per cubic meter. Equation 6 is set forth in Skolnick, op. cit., at p. 624. Substituting N=10 /cm. -l0 /m. into Equation 6, it may be seen that f= mHz. Of course, signals at frequencies lower than this also will be reflected from cloud 20.

As noted hereinabove, a number of mechanisms at work in the upper atmosphere tend to reduce the actual number of free electrons available in cloud 20. At higher altitudes, attachment and radiation recombination are the predominating mechanisms. For example, at an altitude of 81 miles reduction in charge density from 10 electrons/cm. to 10 electrons/cm. will occur in about 10 seconds.

At lower altitudes diffusion is the predominating decay process, and is altitude dependent. For example, at an altitude of 56 miles, the time required for an ion cloud to decay from 10 electrons/cm. to electrons/cm. is about 250 seconds, while at an altitude of 50 miles the time required for equivalent reduction in charge concen tration is only 6 seconds. Note that these attachment, radiation recombination, and diffusion charge reduction mechanisms were the primary factors limiting the lifetime of prior art artificial ion clouds produced in the ionosphere by explosive or thermal type reactions.

When artificial ion cloud 20 (see FIG. 1) is produced in the stratosphere, the same charge decay mechanisms are present. However, the attachment and radiation recombination mechanisms merely serve to regenerate the original photoionizable compound. For example, the Li+ and H produced by reaction (I) typically recombine to form LiH, which itself is photoionizable. Thus, in the presence of sunlight the inventive artificial ion cloud 20 tends to regenerate itself, greatly prolonging the lifetime of the cloud. Of course, the cloud still tends to diffuse, so that, even in sunlight, the charge density gradually will diminish. (Note in this regard that the typical density value of electrons/cm. used in the description above generally is applicable to the cloud as formed, and will diminish with time.)

A typical application of an artificial ion cloud produced in accordance with the present invention is to provide a short term VHF transmission path. For example, such a reflective cloud could facilitate television transmission from a portable transmitter to a remote receiving station and would be useful to provide a line TV coverage of a news event from a remote location using a relatively low power portable transmitter. A small rocket, equipped with appropriate microsphere dispensing equipment such as that illustrated in FIG. 1, may be lobed into the stratosphere at an appropriate location between the remote transmitting site and the receiving station. When released, the microspheres would produce an ion cloud of suificiently high reflectivity to permit good TV reception at the receiving station, despite the use of a very low power transmitter.

Although the invention has been described in detail, it is to be understood that the same is by way of illustration and example only, and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. A process for producing an artificial ion cloud, said process comprising the steps of:

releasing in the upper atmosphere :1 compound selected from the class consisting of lithium hydride, sodium hydride, butyl lithium and ethyl cesium.

2. The process defined in claim 1 wherein said compound forms the core of ablative coated microspheres.

3. A process for producing an atificial ion cloud, said process comprising the steps of:

passing a vehicle through the stratosphere, and releasing from said vehicle ablative coated microspheres of a compound selected from the class consisting of lithium hydride, sodium hydride, butyl lithium and ethyl cesium.

4. The process defined in claim 3 wherein said microspheres are released as said vehicle passes through the ozone layer.

5. The process defined in claim 3 wherein said microsphres are coated with low melting microcryystalline wax.

6. The process defined in claim 3 wherein said cloud is produced in sunlight.

7. An apparatus for producing an artificial ion cloud comprising:

a vehicle adapted for passage through the stratosphere,

means, situated on said vehicle, for releasing ablative coated microspheres from said vehicle during passage through the stratosphere, said microspheres comprising a compound selected from the class consisting of lithium hydride, sodium hydride, butyl lithium, and ethyl cesium.

8. An apparatus as defined in claim 7 wherein said microspheres each are coated with an ablative microcrystalline wax.

9. An apparatus as defined in claim 7 wherein said means comprises:

a reservoir for storing said microspheres,

nozzle means for emitting said microspheres from said vehicle, and

means for withdrawing said microspheres from said reservoir and for providing said microspheres to said nozzle means at a controlled rate.

10. As a material for producing an artificial ion cloud in the stratosphere, ablative coated microspheres of a compound selected from the class consisting of lithium hydride, sodium hydride, butyl lithium or ethyl cesium.

References Cited UNITED STATES PATENTS 2,871,344 1/1959 Busignies 343-18 3,068,472 12/1962 DellAria 343-18 3,150,848 9/1964 Lager 343-18 3,151,325 9/1964 Komptner 343-18 3,189,901 6/1965 Cutolo 343-18 3,249,474 5/ 1966 Clay et a1. 149-6 3,377,955 4/1968 Hodgson 149-6 X OTHER REFERENCES Gladych, Operation Smoke Puff, Popular Mechanics, October 1958, pp. 114, 115, 254.

RODNEY D. BENNETT, JR., Primary Examiner B. L. RIBANDO, Assistant Examiner US. Cl. X.R. 

